The present invention relates to molding compositions containing a polycondensation product of a polyamide, a polyester and a specific compatibility and adhesion promoter.
Multilayer composites consisting of polyamides and either polyesters or polycarbonates are of great practical, commercial and scientific interest since these materials have characteristics which cannot be achieved with a single thermoplastic resin. Distinctly improved characteristics such as lower water absorption, improved resistance to stress cracking, a high degree of toughness and good dimensional stability can be obtained with blends of polyamides and polyesters and with blends of polyamides and polycarbonates which are otherwise unattainable. However, polyamides are, as a rule, not miscible with polyesters or polycarbonates. Therefore, suitable agents for imparting compatibility or for promoting adhesion must be used in blends and in multilayer composites containing these resins.
Blends of polyamides with polyesters or polycarbonates containing agents for imparting compatibility have already been described: specific amorphous polyamides (U.S. Pat. No. 4,798,874), malemide copolymers (EP-A-361 230), high molecular weight epoxy compounds (German Offenlegungsschrift 3,833,286), styrene copolymers (German Offenlegungsschrift 3,832,849) or hydroxyl group-containing polymers (German offenlegungsschriften 3,641,499 and 3,605,573). Random copolycondensation products of polyamides and polyesters are disclosed in U.S. Pat. No. 4,788,249 which are prepared from the monomers and cannot be produced by simple melt-mixing of the polycondensation product components. Moreover, the producibility of the copolycondensation products is restricted to specific systems.
Copolycondensation products of polyamides and polyesters are described in U.S. Pat. No. 4,417,031. Here, polyamides and polyesters are mixed in the melt phase with the addition of one or more phosphite catalysts. In WO 90/12836 aryl phosphoryl azides are described as catalysts for improving the compatibility between polyamides and polyesters. A disadvantage of this process, however, is that the catalyst remains in the composition and is the cause of further uncontrollable reactions, such as the increase or decrease in molecular weight or the accelerated degradation by hydrolysis during processing.